CA1120460A

CA1120460A - Lubricant for metal strip

Info

Publication number: CA1120460A
Application number: CA000310673A
Authority: CA
Inventors: Rudolf Baur
Original assignee: Schweizerische Aluminium AG
Current assignee: Alcan Holdings Switzerland AG
Priority date: 1977-09-06
Filing date: 1978-09-05
Publication date: 1982-03-23
Also published as: ATA642378A; NL7809079A; BE870259A; CH633039A5; NO153323C; FR2401985A1; FR2401985B1; GB2003924B; SE443575B; AT366408B; NO153323B; DE2742290A1; DK390478A; NO783008L; DK154570B; IT7827378A0; US4228217A; IT1098553B; DE2742290B2; SE7809317L

Abstract

ABSTRACT

A lubricant composition for metal strip comprises as lubricating agent an aluminum or magnesium salt of a saturated C11 to C19 monocarboxylic acid, or a mixture of such aluminum and magnesium monocarboxylic acid salts, in admixture with at least one dispersion agent suitable for depositing the lubricating agent on a surface of the metal strip from a dispersion, the lubricating agent is present in an amount of at least 60 weight % based on the total weight of the composition. The lubricant composition of the invention is particularly suitable for blank and painted strips made of aluminum or aluminum alloys and used for packaging, in particular for the packaging of foodstuffs.

Description

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BACKGROU~D OF THE I~VE~TIO~
The invention concerns a lubricant for metal strip, in particular for blank and painted s-trips made of aluminum or aluminum alloys and used for packaging, in particular for the packaging o foods-tuffs.
Containers which can be used in the packaging of foodstuffs and the like, can be produced in a conventional manner by deep drawing material such as aluminum strip which is generally blank or painted before this operation. In order that the strip can be readily processed in various subsequent operations, the surface of the strip must exhibit good slip properties. Depositing a lubricant on the surface of the strip in one oE the production steps (after painting, for instance) produces the desired effects. The surfaces bearing a lubricant must meet the following requirements:
a) The ease of slip between two surfaces with a lubricant on them must be as great as possible, b) Ease slip must be maintained for a long time, more than two years, for instance. The substan-ce providing easy slip must be able to with-stand air, oxygen and light under normal storage conditionsand must not lose its lubricating properties.
c) The lubricating effect of the slip promoting agent must be so good that the material bearing the lubricant can be used, without any addition-al lubricant, for the production of containers by deep drawing.
d) The lubricant must not give off any smell. In particular, the blank or painted thin strip ~ 46~

produc-t bearing the lubricant must not give off any smell when heated. In other words, the lubri-c~nt must exhibit thermal stability.
e) The coating of lubricant must prevent the contents from sticking to the sheet, even after relatively strong heating, such as in baking.
f) The coating of lubricant on baked lacquer coated strip may alter the thermal sealing characteris~
tics only to a controllable degree~
g) The Lubricant must not react with lacquer coatings and must not cause swelling or dissolution o lacquer coatings. The components making up the lubricant must be in full accordance with the laws concerning foodstuffs.
The fluid substances used as lubricants up to now, such as paraffin oil and synthetic trlglyceride, fulfill the above requirements only in part.
Furthermore, in some countries efforts are being made which would to a large degree prevent paraffin oil from being used as a lubricant on containers for foodstuffs.
SUMMARY OF THE I~IVE~TION
Therefore, the inventor has developped the surface lubricant of the present invention whlch satisfies the above-listed requirements. In addition, the lubricant of the pre-sent invention exhibits no toxic effects and thus enjoys the approval of the laws covering foodstuffs.

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In accordance wi-th the present inven-tion, there is thus provided a lubricant composi-tion for metal strip used for packaging purposes, which comprises as lubricating agent an aluminum or magnesium salt of a saturated C11 to Clg mono-carboxylic acid, or a mixture of suchaluminum and magnesium monocarboxylic acid salts, in admixture with at least one dispersion agent suitable for depositing the lubricating agent on a surface of the metal strip from a dispersion, the lubricating agent being present in an amount of at least 60 weight % based on the total weight of the composition.
The invention further provides a metal strip having at least one side thereof coated with a lubricant composition as defined above, wherein the strip is suitable for c~ating or laminating on one or both sides.
The appropriate stearate of aluminum or magnesiwn monocarbonic acid salt has been ~ound to be particularly advantageous.
Extensive plant trials also show that alu~inum tri-stearate in most cases produces a somewhat better lubricating 2~ effect than magnesium di-stearate. rrhe lubricating properties of magnesium di-stearate, on the other hand, are signlficantly better than those of the rest of the alkali-earth di-stearates.
Research also shows, however, that aluminum and magnesium monocarbonic acid salts can be applied on an indus-trial scale only with great difficulty.
In an advangageous embodiment of the lubricant of the present invention, these difficulties can be overcome, at least in part, by the addition of application agents. Surpri-singly, research indicates that, in the use of mi~tures of aluminum and magnesium monocarbonic acid salts, the small quantity of monocarbonic acid salt added as an application 04~0 agent to assist in application of the lubricant i~ not suit-able as -the main constituent of the lubricant of the invention comprising mainly other monocarbonic acids.

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Both monocarbonic acid salts can thus be used in any mixed ratio desired. Using basically the following mixtures (-~eight %), however, has been found most advantageous for lubricants:
85 - 95%, preferably 89 ~ 94% of an luminum salt of a saturated Cll to Clg monocarbonic acid, and 5 - 15%, preferably 6 - 11% of a magnesium salt of a saturated Cll to Clg monocarbonic acid, or 85 - 95%, preferably 89 - 94% of a magnesium salt of a saturated Cll to Clg monocarhonic acid, and 5 - 15%, preferably 6 - lla/o of an aluminum salt of a saturated Cll to Clg monocarbonic acid.
The use of mixtures of alurninum and magnesium mono-carbonic acid salts affect the lubricating properties of the main component of the ]ubricant of the invention only insignificantly. Usefully, the same monocarbonic acid, stearic acid for exarnple, is employed for the main constituent of the lubricant as for the application agent' ho~e~er, mixtur~ such as the following can also be used:
a~uminurn stearate as the main constituent of the lubricant and magnesium di-laurate as the application agent; or magnesium di-stearate as the main constituent of the lubricant and aluminurn tri-laurate as the application agent.
The rnetal strip intended for packaging purposes is, in many cases, coated with lubricant immedlately after the lacquering, Thus, it had to be determined whether the lu-bricant of the present invention could be deposited on the ~1~0~6~

surface of the strip fram a solution or a dispersion from analiphatic solvent such as is normally used in lac~uering technology, n-hexane, for instance.
This requirement causes difficulties in that neither the magnesium salts of long chain monocarbonic acids nor a mixture of both are soluble or dispersible in large quanti-ties in aliphatic slovents. But these problems can be over-come by the addition of a further application agent, namely a dispersion agent. The following classes of substances have ; 10 proved of value as - synthetic triglycerides, , - paraffin oils, ;~ - poly-isobutenes, ; - aliphatic C~ to C16 alcohols, ~ - esters of a methyl or ethyl alcohol with a Cll to ,~ ` C17 monocarbonic acid, ~ - estersof a C3 to C6 alcohol with a saturated Cll to ,:
C17 monocarbonic acid, esters of an aliphatic Cl to C6 alcohol with a W -oxy-monocarbonic acid.
The methyl and ethyl esters of the Cl1 to C17 mono-carbonic acids, particularly lauric acid, have proven especially useful.
Table IA presents examples of the compositions of two lubricants conforming to the present inventio}l. Naturally the listed substances in Table IA, aluminum tri-stearate, magnesium di-stearate and methyl palmitate, can be replaced by other members of their groups of substances in accordance with the present invention as shown in Table IB.

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TABLE IA

Composition No. lA Composition No. 2A
Lubricant Component!wt /O) _ (w-_ %

Aluminum tri-stearate60-80 2-.10 Magnesium di-stearate2-10 60-80 Methyl palmitate 10-30 10-30 TABLE IB
Composition No.lB Cornposition No. 2B
Lubricant Component(wt %) (wt %) 10 Aluminum salt of a60-80 2-10 saturated Cll to Clg monocarbonic acid Magnesium salt of a2-10 60-80 saturated Cll to Clg monocarbonic acid Dispersi.on agent 10-30 10-30 Liquid aliphatic hydrocarbons, in particular n-hexane, which are often used as solvents in lacquer technology, have been found to be particularly suitable for the preparation of dispersion of the lubricant of the present invention.
This solvent boils at 69C, gives off almost no smell and, in particular in coats of lacquer, causes no microscopic brittle cracks as can be observed in many cases when aliphatic alco-hols or aliphatic ketones are used as solvents. The amounts of n-hexane taken up by the lacquer during the coating of the lacquered strip with the lubricant of the present inven-tion are small and are to a large extent evaporated off by the subsequent drying. Thus, the residual amount of solvent hardly affects the lacquer coating. When coating blank metal strip, however, aliphatic alcohols or ketones can also be '~-~12~6~) used. Their use, thc.ugh, is preferably limited to the treatment of blank strip since they, as mentioned above, can cause microscopic brittle cracks in the lacquer.
By using the dispersions prescribed by the invention, exceptionally stable dispersions can be formed in aliphatic solvents. Some dispersions tend to settle as a precipitate to a certain degree after standing for a while. In these substances, the precipitated particles of the metal salts of long chain monocarbonic acids can be immediately agitated into suspension again by means of only the slightest arnount of stirring.
These dispersion agents have~been~found to a certain degree to cause unpleasant odors on heating (e.g., baking) lubricants, in particular those intended for food packaging.
These odors are partly due to impurities in the dispersion agent. Therefore, it is extremely irnportant to use dis-persion agents which are at least of the grade "purified" in the preparation of lubricants for foodstuff packaging. Lu-bricants containing methyl and ethyl esters of the saturated Cll to C17 monocarbonic acids, either individually or mix-tures thereof, have been shown to be particularly suitable ~; for foodstuff packaging. The preferred dispersion agent is methyl palmitate. ~ ~
Substances of the rest of the classes of such chemicals can be more usefully employed for~packaging strip used for applications other than the packaging of foodstuffs.
Table II shows a typical and particularly useful composition of a dispersion agent for the surface lubricant of the invention.

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TABLE II
Range Preferred Range Di~eersion Component (wt %) (wt %) Aluminum tri-stearate 2.5-10.0 ~0-6.5 Magnesium di-stearate 0.1-1D 5 0.3~0.7 Methyl palmitate 0.8-3.0 1.2-2.0 n-hexane 85.5-96.6 91.Q-94O0 Such a dispersion exhibits excellent stability even after standing for several months, displaying only very slight precipitation.
A further similarly advantageous composition of the dispersion in accordance with the present invention can be obtained when the concentrated ranges in Table II for alumi-num tri-stearate and magnesium di-stearate are reversed.
These dispersion agents, which represent a component of the lubricant on the metal strip after drying, also exhi-bit a certain degree of lubrication. With these agents, however, the degree of lubrication is not as pronounced as that of the aluminum and magnesium monocarbonic acld salts~
Furthermore, this property may lessen in the course of time due to oxidation of the dispersion agent. In extreme cases, in particular with tri-glycerides, oxidation of the disper-sion agent can result in the conversion of the luhricant into a sticky film which makes the sheet coated with the substance unusable. In these case, the duration, that is, the period of time which these lubricants containing oxida-tion sensitive dispersion agents are allowed to stand, can be extended by the addition of at least one further additive, a so called oxidation inhibitort Such alterations have been so successful that these oxidation sensitive dispersion a61) agents can also be employed on an industrial scale. The oxidation inhibitors are usefully added in quantities equal to that of the dispersion agent. There are, however, com-positions of lubricants in which the concentration of oxi-dation inhibitors is larger or smaller thant that of the dis-persion agent. Such compositions are not only usable but, in some cases, are even advantageous. Palmitoyl ascorbate is one such oxidation inhibitor.
Only those lubricants which contain dispersion agents which are suitable for foodstuff packaging, i.e., methyl and ethyl ester saturated Cll to C17 monocarbonic acids, show no changein the lubricating properties due to oxidation o-f the dispersion agent.
m e dispersion can be prepared by adding the compo-nents of the lubricant, i.e., the aluminum and magnesium -monocarbonic salts, the dispersion agent and the anti-oxi-dation agent to a solvent. The resulting mixture is then heated for a long period of time, such as 6 to 8 hours, in a reflux apparatus in such a way that the solvent boils continuously. A milk white dispersion of swollen metal stearate particles in the solvent results. In extreme cases, such as when employing special dispersion agents, a solution may be obtained. The deposition of the lubricant on the surface of the strip can take place using the usual methods and equipment employed in lacquer technology. Processes and devices for immersion coating or varnishing have been found to be favorable for this purpose. Thus, the packaging strip is, by way of preference, coated on both sides with the lubricant of the invention.
The packaging industry usually employs aluminum and its alloys in the form of strip which can be coated on one i, ~ .

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or bo-th sides with lacquer or else laminated with another material. rrhe thickness of these aluminum alloy strips varies, depending on the application, from lO to 250 ~m.
The thickness of the lacquer or laminate coating of one or, if desired, both sides of the strip is preferably between l and lO0 ~m.
The amount of lubricant deposited must be chosen with the later processing of the strip in mind. Preferably, each side receives between lO and 150 mg/m2. If the strip is to be used for the packaging of foodstuffs, then the appropriate legal specifications must be taken into account when determining the amount of lubricant to be deposited.
When used on blank and lacquered strip material, the lubricant of the in~ention satisfies all the require-ments set by the packing industry, in par-ticular:
a) The manufacture of deep drawn containers without application of additional lubricants before or during the shaping process.
b) Agent to allow stamped out, stacked metal lids to be separated individually on the assembly line automatically and without difficulty.
c) Separating agent for baked products (in part-icular products with a high sugar content) to allow easy removal of the contents, such as from an aluminum mold or tray after ~aking.
d) Easy removal of stacked metal sheet used as blanks for the production of folded containers~
e) Application as a lubricant for aluminum foils and strips to be processed further by unloading from coil form by equipmentl as for wrapping for chocolate and the like.

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Deep drawn packaging containers made from lacquered or laminated aluminum s-trip, coated wi-th the lubricant accord-ing to the present invention, can be sealed tight with a lid in the normal manner by means of heat sealing. Th:is process differs from sealing done with conventional paraffin oil based lubricants only in that in certain cases it requires a slightly higher sealing temperature to achieve airtight sealing of the package. This requirement can be met on industrial packaging machines sim~ly by raising the -tempera-ture and without any kind of difficulty arising and withoutincurring any disadvantage.
Figures 1 and 2 show schematically two devices which are particularly favorable for applying the lubricant of the invention to 5 trip material.
Figure 1 shows a device comprising an uncoiling roll 1, a container 2 holding the dispersion, squeeze rolls 3, drying tunnel 4 with an exhaust pipe fitted with a fan to draw off the solvent vapor 5, circular knife-edge with backing 6 and a spool 7 on which the strip, coated with lubricant and trimmed, is coiled.
The quantity of lubricant deposited on the strip can be regulated by means of the squeeze rolls, one of which is made of s-teel, the other of rubber, fitted with facilities for pneumatic or mechanical adjustment of the pressure between them. When using n-hexane as solvent, the temperature in the drying tunnel is about 80 C.
Figure 2 shows schematically a conventional lacquering device which has also been found to be particularly suitable for coating strip with the lubricant of the present invention.
The device comprises an uncoiling roll 1, a bath 2 containing ~r \~

d~6~0 the dispersion, squeeze rolls 3, drying tunnel ~ with exhaust pipe and fan 5, and a roll 6 for coiling the strip which has been coated on both sides. As in the device shown in Fig. 1, the squeege rolls 3 are preferably made of steel and/or rubber and the temperature in the drying tunnel is preferably around 80C when using n-hexane as the solvent.
The squeeze rolls 3 are also provided with facilities for adjusting them mechanically. l~us, the amount of lubricant deposited on the sheet can be controlled.
Thus, a controlled amount of said lubricant can be applied to both sides of said strip by passing said strip through a bath of said lubricant to provide a lubricant coated strip and thereafter passing said lubricant coated strip through squeeze rolls to regulate the amount of lu-bricant remaining on said strip.
The following examples illustrate the advantages of the lubricant of the present invention.
EXAMPLE I
The effect of various dispersion agents will be illustrated using a lubricant of the following compos:ition:
aluminum tri-stearate 91%
magnesium di-stearate 9%
The manner o~ testing was that 5.5 g of lubricant was added together with a specific amount of dispersion agent to 94.5 g n-hexane, and the resulting mixture boiled for 7 hours in a reflux apparatus.
The results given in Table III demonstrate the stability of the dispersion over a period of 30 days at 25C, the degree of lubrication provided between two sheets o~
aluminum and the extent to which odor is produced by the `! -12-~ j ~'r~

coated aluminum when heated to 60C for 60 minutes.
The stability of ~le dispersion i9 arbitrarily de~ined as follows:
A stability of 100% means that ~le dispersion did not change during the entire test period~
A stability of 70% means that 30 vol.% comprised clear n-hexane above the dispersion.
A stability of 0% indicates that the dispersion has settled out in precipitate form.
The results presented ln Table III show that usable lubricants can be obtained using all the dispersion agents listed. Clearly, though, methyl palmitate, i.e,dispersion agents of the group "esters of a Cl or C2 alcohol with a saturated Cll to C17 monocarbonic acid", can be employed as constituents of a lubricant for food-packaging strip.
Furthermore, Table III shows that adequate lubrication can be achieved with all the dispersion agents, the amount of dispersion agent present being of no great significance.
The degree of lubrication is classified in Table III as:
; ~ 20 excellent, very good, good, poor, very poor.

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EXAMPLE II
A lubricant of the following composition:
aluminum tri-stearate 5 wt %
magnesium di-stearate 0.5 wt %
methyl palmitate 1.5 wt %
was deposited on a blank aluminum strip using a device corresponding to that shown in Fig. 1. For this purpose, the lubricant of the above composition was boiled for 7 hours in a reflux apparatus in 93 wt % n-hexane as was already described earlier.
The dispersion produced -this way was deposited on both sides of the aluminum strip in different quantities, which were then measured. The results are presented in Table IV.

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The regulations of the Food and Drug Administration permit aluminu~ tri-stearate and rnagnesium di-stearate to be in contact with foodstuffs, provided they do no-t exceed 310 mg/m2 in quantity.
Similarly, the Food and Drug Administration allows deposits of methyl plamitate up to 23 mg/m .
Table IV shows that the lubricant of the present invention containing methyl paLmitate as dispersion agent complies with the legal requirements, when the coating on the strip coming into contact with the contents exceeds a value of around 100 mg/m /side.
This invention may ~e embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodi-ment is therefore to be considered as in all respects illustrative and not restrictive, the scope oE the invention being indicated by the appended claims, and all changes which come within the rneaning and range of equivalency are intended to be embraced therein~

Claims

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:-l. A lubricant composition for metal strip used for packaging purposes, which comprises as lubricating agent an aluminum or magnesium salt of a saturated C11 to C19 mono-carboxylic acid, or a mixture of said aluminum and magnesium monocarboxylic acid salts, in admixture with at least one dispersion agent suitable for depositing said lubricating agent on a surface of said metal strip from a dispersion, said lubricating agent being present in an amount of at least 60 weight % based on the total weight of the composition.
2. A lubricant according to claim l, wherein said lubricating agent comprises aluminum tri-stearate or magnesium di-stearate, or a mixture thereof.
3. A lubricant according to claim l, wherein said lubricating agent comprises a mixture of:
85-95 wt.% of an aluminum salt of a saturated C11 to C19 monocarboxylic acid, and 5-15 wt.% of a magnesium salt of a saturated C11 to C19 monocarboxylic acid.
4. A lubricant according to claim 3, wherein said lubricating agent comprises a mixture of:
89-94 wt.% of an aluminum salt of a saturated C11 to C19 monocarboxylic acid, and 6-11 wt.% of a magnesium salt of a saturated C11 to C19 monocarboxylic acid.
5. A lubricant according to claim 1, wherein said lubricating agent comprises a mixture of:
85-95 wt.% of a magnesium salt of a saturated C11 to C19 monocarboxylic acid, and 5-15 wt.% of an aluminum salt of a saturated C11 to C19 monocarboxylic acid.
6. A lubricant according to claim 5, wherein said lubricating agent comprises a mixture of:
89-94 wt.% of a magnesium salt of a saturated C11 to C19 monocarboxylic acid, and 6-11 wt.% of an aluminum salt of a saturated C11 to C19 monocarboxylic acid.
7. A lubricant according to claim 1, wherein said lubricating agent comprises a mixture of said aluminum and magnesium salts and wherein the aluminum salt and the magnesium salt are salts of the same monocarboxylic acid.
8. A lubricant according to claim 1, wherein said dispersion agent is present in an amount of from 10 to 30 weight %.
9. A lubricant according to claim 8, comprising a mixture of:
60-80 wt.% of an aluminum salt of a saturated C11 to C19 monocarboxylic acid;
2-10 wt.% of a magnesium salt of a saturated C11 to C19 monocarboxylic acid; and 10-30 wt.% of at least one dispersion agent.
10. A lubricant according to claim 8, comprising a mixture of:
60-80 wt.% of a magnesium salt of a saturated C11 to C19 monocarboxylic acid, 2-10 wt.% of an aluminum salt of a saturated C11 to C19 monocarboxylic acid, and 10-30 wt.% of at least one dispersion agent.
11. A lubricant according to claim 1, wherein said dispersion agent is selected from the group consisting of:
- synthetic triglycerides;
- paraffin oils;
- poly-isobutenes;
- aliphatic C4 to C16 alcohols;
- esters of a methyl or ethyl alcohol with a C11 to C17 monocarboxylic acid;
- esters of an aliphatic C3 to C6 alcohol with a saturated C11 to C17 monocarboxylic acid;
- esters of a C1 to C6 alcohol with a .omega.-oxymono-carboxylic acid; and - mixtures thereof.
12. A lubricant according to claim 11, wherein said dispersion agent is a methyl or ethyl ester of a saturated C11 to C17 monocarboxylic acid or a mixture thereof.
13. A lubricant according to claim 12, wherein said dispersion agent is methyl palmitate.
14. A lubricant according to claims 11, 12 or 13, wherein said dispersion agent is present in an amount of from 10 to 30 weight %.
15. A lubricant according to claim 11, wherein said dispersion agent contains a solvent selected from the group consisting of liquid aliphatic hydrocarbons, aliphatic alcohols, and aliphatic ketones.
16. A lubricant according to claim 15, wherein said solvent is n-hexane.
17. A lubricant according to claims 11, 12 or 13, further comprising an oxidation inhibitor.
18. A lubricant according to claim 8, wherein said lubricating agent comprises aluminum tri-stearate or magnesium di-stearate, or a mixture thereof.
19. A lubricant according to claim a, wherein said lubricating agent comprises a mixture of:
85-95 wt.% of an aluminum salt of a saturated C11 to C19 monocarboxylic acid, and 5-15 wt.% of a magnesium salt of a saturated C11 to C19 monocarboxylic acid.
20. A lubricant according to claim 19, wherein said lubricating agent comprises a mixture of:
89-94 wt.% of an aluminum salt of a saturated C11 to C19 monocarboxylic acid, and 6-11 wt.% of a magnesium salt of a saturated C11 to C19 monocarboxylic acid.
21. A lubricant according to claim 8, wherein said lubricating agent comprises a mixture of:
85-95 wt.% of a magnesium salt of a saturated C11 to C19 monocarboxylic acid, and 5-15 wt.% of an aluminum salt of a saturated C11 to C19 monocarboxylic acid.
22. A lubricant according to claim 21, wherein said lubricating agent comprises a mixture of:
89-94 wt.% of a magnesium salt of a saturated C11 to C19 monocarboxylic acid, and 6-11 wt.% of an aluminum salt of a saturated C11 to C19 monocarboxylic acid.
23. A lubricant according to claim 8, wherein said lubricating agent comprises a mixture of said aluminum and magnesium salts and wherein the aluminum salt and the magnesium salt are salts of the same monocarboxylic acid.
24. A metal strip having at least one side thereof coated with a lubricant composition which comprises as lubricat-ing agent an aluminum or magnesium salt of a saturated C11 to C19 monocarboxylic acid or a mixture of said aluminum and magnesium monocarboxylic acid salts in admixture with at least one dispersion agent, said lubricating agent being present in an amount of at least 60 weight % based on the total weight of the composition, wherein said strip is suitable for coating or laminating on one or both sides.
25, A metal strip according to claim 24, wherein said strip is aluminum or an aluminum alloy strip for packaging.
26. A metal strip according to claim 25, wherein said strip is 10 to 250 ?m thick.
27. A metal strip according to claim 24, wherein the amount of coating of lubricant on the metal strip is between 10 and 150 mg/m2/side.
28. A metal strip according to claim 24, wherein the aluminum salt and the magnesium salt of the saturated C11 to C19 monocarboxylic acid are salts of stearic acid.
29. A metal strip according to claim 24, wherein the lubricant includes from 10 to 30 weight % of said dis-persion agent.
30. A metal strip according to claim 24, wherein said dispersion agent is selected from the group consisting of:
- synthetic triglycerides;
- paraffin oils;
- poly-isobutenes;
- aliphatic C4 to C16 alcohors;
- esters of a methyl or ethyl alcohol with a C11 to C17 monocarboxylic acid;
- esters of an aliphatic C3 to C6 alcohol with a saturated C11 to C17 monocarboxylic acid;
- esters of a C1 to C6 alcohol with a .omega.-oxymo-nocarboxylic acid; and - mixtures thereof.
31. A metal strip according to claim 30, wherein said dispersion agent is a methyl or ethyl ester of a saturated C11 to C17 monocarboxylic acid, or a mixture thereof.
32. A metal strip according to claim 31, wherein said dispersion agent is methyl palmitate.
33. A metal strip according to claims 30, 31 or 32, wherein the lubricant contains from 10 to 30 weight % of said dispersion agent.
34. A metal strip according to claims 30, 31 or 32, wherein the lubricant further contains an oxidation inhibitor.
35. A metal strip according to claim 32, wherein at least one side of said strip is coated with a lubricant comprising a mixture of:
aluminum tri-stearate 60-80 wt.%
magnesium di-stearate 2-10 wt.%
methyl palmitate 10-30 wt.%
36. A metal strip according to claim 32, wherein at least one side of said strip is coated with a lubricant comprising a mixture of:
magnesium di-stearate 60-80 wt.%
aluminum tri-stearate 2-10 wt.%
methyl palmitate 10-30 wt.%
37. A metal strip according to claim 24, wherein both sides of said strip are coated with a controlled amount of said lubricant, by passing said strip through a bath of said lubricant to provide a lubricant coated strip, and thereafter passing said lubricant coating strip through squeeze rolls to regulate the amount of lubricant remaining on said strip.
38. A metal strip according to claim 37, wherein two squeeze rolls are provided, one of which is steel and one of which is rubber.
39. A metal strip according to claim 37, wherein the strip is passed through a drying tunnel maintained at an elevated temperature after passing through said squeeze rolls.
40. A metal strip according to claim 39, wherein said drying tunnel includes an exhaust fan for vapor removal.